In the manufacture of paper and paperboard, and of products made from paper and paperboard, petroleum derived paraffin waxes and synthetic polymers have been used for many years as moisture retardants, water repellents, oil repellents, stiffeners, strengtheners, and release agents. Besides paraffin, the material used most often is probably polyethylene, but other widely used polymers include polymerized acrylics, vinyls, styrenes, ethylenes and copolymers or hetero-polymers of these monomers. For example, a polyester resin coating is described in U.S. Pat. No. 5,858,551 to Robert Keith Salsman. The paper and paperboard to which these traditional materials are applied becomes difficult and often impossible to repulp and recycle in standard paper mill processes because the petroleum derived polymers and, particularly, the petroleum waxes are non-biodegradable in mill white waters (circulated process waters) and discharge effluents, and the residue of the petroleum waxes that is not removed from pulp fibers during the repulping and recycling processes cause severe problems due to buildup that occurs on the screens and felts used during the process of forming and making the paper or paperboard sheet. In addition, paper and paperboard coated or impregnated with petroleum waxes resist biodegradation and composting when disposed of in landfills and other waste disposal systems. Paper and paperboard coated or impregnated with traditional synthetic polymers and hetero-polymers are also difficult and often impossible to repulp and recycle owing to their resistance to separation from the fiber in the standard repulping processes resulting in significant fiber losses in efforts to repulp and recycle them, and these are also non-biodegradable and therefore resist composting.
Accordingly, it is one object of the present invention to provide an improved method of waterproofing a paper product, particularly paperboard products with fluted media.
In the past, vegetable oil triglycerides have been used as coating lubricants for paper coatings in starch-based emulsions as described in U.S. Pat. No. 6,201,053 and in U.S. Pat. No. 6,103,308. A hot melt liquid used as a coating is described in U.S. Pat. No. 6,485,742 B1 which issued to Kakeguchi et al. While such emulsion coatings may provide some degree of water resistance, it is an object of the present invention to provide improved waterproofing and wet strength in starch based adhesive.
In another prior art patent, namely, U.S. Pat. No. 6,201,053 the use of a partially saponified triglyceride (PST) is disclosed where the PST may be a thickening agent, surfactant, water proofing agent, or coupling where PST consists of a homogeneous mixture of a metal salt, a fatty acid of said triglyceride, and a mixture of monoglyceride, diglyceride and triglyceride in the absence of a compatibilizing agent. These PST's are said to be useful as lubricants for paper surfaces and can act as water repellants but this process is one of saponification and not hydrogenation. Accordingly, it is another object of the present invention to provide an environmentally compatible alternative to paraffin wax and other coatings by employing hydrogenated triglycerides.
The foregoing and other objects are achieved by the present invention which is described below in the Summary of the Invention and Detailed Description.